Redeye Idling a motor down in the 650-700 rpm range is not a go thing to start with. OIling of the motor is border line. A motor will internally leak pressure off in the 15-30 psi range. The closest parts getting the pressure you read on your dash gauge to the farest point of the motor getting maybe just enough to float the bearings. IF the
oil has oiling modifications this could be even worst. Most motors get too much
oil to the heads and rockers and stavre out the bottom ends. With modes we keep the
oil down on the rotating assembly more. This helps alot. Other note is solid roller lifters or just solids don't like to be ilded at all. Hydro roller will last 200 k miles with good maintainance, solid lifter or roller will last from 200 miles to 20k miles and then maybe need rebuild or checking. Alot depends on valve spring pressures and RPM range.
If you want the car louder, change the mufflers to spirals or straight pipes. Overlap of the camshafts are partially what makes the nasty noise. I think thumper cams would make what you want.
With radiator out of car, camshaft cam be done in the car with loose motor mounts to move it around. Side note, For the time it takes to remove and install the motor and do this on an engine stand will save your back 10 fold. Prelube everything and run motor for 15 minutes at 2,000 rpms for brake in, no exceptions, change oil and filter and look for any metal partials in filter. You should be goto go. Rick L.